Cutting element having a self sharpening tip

ABSTRACT

A cutting element including a shank portion and a conical cutting portion. The conical cutting portion has a narrow end and a broad end connected to the shank portion. The conical cutting portion narrow end has an insert receiving recess, and an insert is secured in the insert receiving recess. The insert has an outer layer made of tungsten carbide, and an inner core made of a material with a greater hardness than the outer layer.

BACKGROUND OF THE INVENTION

This invention relates to cutting elements or bit members or picks andis particularly concerned with such elements having a pointed end thatmakes contact with the material to be cut. Such cutting elements aretypically called a rotary cone bit of the pick type.

A cutting element or pick or bit member according to the presentinvention is a member somewhat like the cutting bit in a machine tooland having a metal body with a hard region or a hard insert therein atthe place where the bit member engages the work. Such bit members arewell known in many industries, such as in the mining industry andusually comprise a steel body, such as forged steel, with a cementedtungsten carbide tip or insert secured thereto as by brazing. The tipusually ends with a small radius and thus is easy to penetrate into thematerial being cut. As the carbide wears, the tip rounds off or dullsslowing penetration into the material to be cut.

Some bit members have been made with one or more layers ofpolycrystalline diamond or a diamond and carbide mixture, coating theexposed part of the bit tip. However, the diamond coating is brittle andflakes off except under the easiest cutting conditions.

SUMMARY OF THE INVENTION

One of the principal objects of the invention is to provide an improvedcutting element that maintains its hard tip longer than with currentcutting elements, and which tends to remain pointed or sharp as thecutting element wears.

The cutting element of the invention has a bit tip with a diamond (orother material harder than the grade of carbide making up the rest ofthe bit tip) core on the cylindrical axis of the bit tip. The toughercarbide on the outside will protect the brittle diamond from impact. Thediamond exposed at the tip will protect the carbide from excessive wear.As the diamond and carbide wear together, they should provide a selfsharpening action.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a bit holding apparatus.

FIG. 2 is a partial cross-sectional view of the bit shown in FIG. 1,with a hardened insert at the end of the bit according to the presentinvention.

FIG. 3 is a cross sectional view of an alternate embodiment of theinsert at the end of the bit shown in FIG. 2.

Before one embodiment of the invention is explained in detail, it is tobe understood that the invention is not limited in its application tothe details of the construction and the arrangements of components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. Use of “including”and “comprising” and variations thereof as used herein is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items. Use of “consisting of” and variations thereof as usedherein is meant to encompass only the items listed thereafter andequivalents thereof. Further, it is to be understood that such terms as“forward”, “rearward”, “left”, “right”, “upward” and “downward”, etc.,are words of convenience in reference to the drawings and are not to beconstrued as limiting terms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for purposes ofillustrating the present preferred embodiments of the invention only andnot for purposes of limiting same, the Figures show a mining machinecutting drum (not shown) which supports a cutting bit 12 by means of abit holder 18.

As is well known in the art, the cutting drum (not shown) is supportedby a mining machine (not shown) for rotation while being verticallymoveable and while the mining machine advances forward. As is also wellknown, the cutting drum (not shown) typically includes a plurality ofcutting bits 12 arranged thereon; however, the present description willnow be directed to a single cutting bit 12 and the structure of a singlepresent bit holder 18.

The bit holder 18 may be attached directly or indirectly to the drum 10.For example, the bit holder may be welded or clamped to the drum 10 ormay be secured to a mounting block attached to the drum 10. As describedhereinafter, the bit holder 18 receives and retains a sleeve 50 whichrotatably receives the bit 12.

The cutting element or bit 12 includes a central cylindrical shankportion 24 and having an enlarged conical cutting portion or nose 26attached thereto such that a shoulder area 28 is formed there between.The cutting bit has a central axis shown at 29 with a hard cutting tip30 on one end of the cutting bit 12. The cutting bit 12 includes on itsother end a recessed notch 32 and terminates in an end shoulder 34 suchthat a retaining ring (not shown) may be received within the notch 32 toprevent the axial removal of the cutting bit 12 from a sleeve 50. Inother embodiments (not shown), the shoulder area 28 can be omitted.

The bit holder 18 has a body portion 38 and a base portion 40. The baseportion 40 attaches directly to the cutting drum (not shown) orindirectly by means of a mounting block (not shown). The body portion38, which is integral to the base portion 40, includes an aperture 42for receiving a coaxial sleeve 50. The aperture 42 defines an innersurface 42 a. The body portion 38 includes a contact face 44 which isshown as perpendicular to the longitudinal axis 46, which is the same asthe central axis 29 of the aperture 42, but which may also be formed asa cone whose surface is at an angle with respect to the longitudinalaxis 46 of the aperture 42.

The sleeve 50 has an elongated body member 52 and a collar 54, thecollar 54 having an inside surface 56 and an outside surface 58. Theinside surface 56 of the collar 54 abuts the contact face 44. The collar54 is shown as having an inside surface 56 which is perpendicular to thelongitudinal axis 46 of the aperture 42; however, the inside surface canbe conical having a conical surface at an angle with respect to thelongitudinal axis 46 corresponding to the angle of the contact face 44.The outside surface 58 of the collar 54 has a beveled surface 60 and aflat surface 62. The body member 52 of the sleeve 50 defines an outersurface 52 a.

The body member 52 of the sleeve 50 has a bore 64 which is coaxial withthe bit axis 29. The bit 12 is rotatably received by the bore 64. Theshank 24 of the bit 12 is slightly smaller than the bore 64. The shank24 is retained in the bore 64 by the retaining ring and the shank mayrotate about the central axis 29 in order to avoid uneven wearing of thetip 30 of the cutting bit 12. The shoulder area 28 of the bit 12 abutsthe flat surface 62 to position the bit 12 axially in the bore 64 andtransmit cutting forces.

More particularly, as shown in FIG. 2, the conical cutting portion 26has a narrow end 70 and a broad end 74 connected to the shank portion24. The conical cutting portion narrow end 70 has an insert receivingrecess 78, and the hard cutting tip or insert 30 is secured in theinsert receiving recess 78, such as by brazing. The insert 78 has anouter layer 82 made of tungsten carbide, and an inner core 86 on thecylindrical axis 29 (see FIG. 1) of the conical cutting portion 26. Theinner core 86 is made of a material with a greater hardness than theouter layer 82. Preferably, the insert 30 has a cylindrical portion withthe outer end 90 of the insert 30 having a small radius so that theouter end 90 forms a point for aiding in cutting material.

In the preferred embodiment, the inner core 86 is made of diamond, butin less preferred embodiments, a hardened form of tungsten carbide canbe used. The diamond core 86 is a solid diamond, not a coated structure.Further, in the preferred embodiment, the inner core 86 is exposed atthe outer end 90. The inner core 86 is made from a sheet of material,but in other embodiments (not shown), the inner core 86 may becylindrical, or any other shape. Further, in an alternate embodiment, asshown in FIG. 3, the insert 94 can include a second layer or core 96with a hardness between that of the outer layer 82 and the inner core86, or even more layers or cores. In order to obtain the advantage ofmaintaining the small radius at the insert outer end 90, each more innerlayer in the insert 30, going from the outside of the insert 94 to theinside, should be harder than the preceding more outer layer.

Various other features and advantages of the invention will be apparentfrom the following claims.

1. A cutting element including a shank portion, a conical cuttingportion, the conical cutting portion having a narrow end and a broad endconnected to the shank portion, said conical cutting portion narrow endhaving an insert receiving recess, and an insert secured in said insertreceiving recess, said insert having an outer layer made of tungstencarbide, and an inner core made of a material with a greater hardnessthan the outer layer.
 2. A cutting element in accordance with claim 1wherein said inner core is made of diamond.
 3. A cutting element inaccordance with claim 1 wherein said insert forms a point at the end ofthe conical cutting portion, and said inner core is exposed at saidpoint.
 4. A cutting element in accordance with claim 1 wherein saidbroad end is wider than said shank portion, forming a shoulder betweenthe conical cutting portion and the shank portion.
 5. A cutting elementin accordance with claim 1 wherein said conical portion has acylindrical axis, and said insert is on the cylindrical axis of saidconical portion.